Nearly all fission reactions utilizing the uranium isotope U.sub.235 require a concentration of the U.sub.235 isotope greater than in the naturally occuring state. U.S. Pat. No. 3,772,519 for METHOD AND APPARATUS FOR THE SEPARATION OF ISOTOPES by R. H. Levy et al. discloses a method for isotope separation in which an environment containing a plurality of uranium isotopes is irradiated with laser radiation of a particular frequency to selectively excite the particles of the desired isotope type, which selectively excited particles may then be separated as disclosed in the patent. For optimum efficiency, the laser isotope separation process, as taught in the Levy patent, prefers excitation radiation with energy distributed throughout the bandwidth of absorption structure of the U.sub.235 component of uranium vapor rather than the series of discrete mode frequencies typical of most laser radiation.
One way of achieving the even energy distribution is to "chirp" or sweep the frequency of the laser radiation, moving the spectral lines so that all portions of the U.sub.235 absorption band are subject to resonant frequency laser radiation. Representative methods of producing such a chirp are shown in U.S. Pat. No. 3,611,182 and U.S. patent application Ser. No. 483,077 filed June 25, 1974 and assigned to the same assignee as the present application.